1. Technical Field
The disclosure relates generally to a cascade device of serial bus devices with clock and management method thereof, and, more particularly to cascade devices and methods capable of cascading and managing multiple serial bus devices, each of which with a clock.
2. Description of the Related Art
With the progress of science and technology, there has been an explosive increase in the use of removable electronic devices or so-called serial bus devices such as data storage devices or Input/Output (I/O) devices within a host device, e.g. an embedded system or electronic device (e.g. hand-held or portable devices including MID, NetBook, personal digital assists (PDAs), tablet personal computers, UMPC, personal computers (PC), Notebooks and so on) for expanding functions of the host device. For example, a removable device with a GPS module capable of providing a navigation function may be plugged into the host device such that the host device can perform the navigation function.
Serial bus devices (e.g. memory cards) may communicate with a host device (e.g. a mobile phone) for data transmission via a bus interface, such as a serial peripheral interface (SPI), a SD or a MMS bus interface. The bus interface has a clock signal and a chip selection signal such that the mobile phone may access to the memory card according to the clock signal when the chip selection signal is enabled.
The serial bus devices, however, require to connect to slots of the host device, wherein each slot may only accommodate a single serial bus device. Generally, as the host device may have only one slot for a serial bus device (e.g. a memory card) to plug into, such a host device may be no longer expanded after one serial bus device has been plugged.
US publication no. 2006/0277333 discloses a portable data storage device that is capable of cascading another portable data storage device, wherein the disclosed portable data storage device adopts an Universal Serial Bus (USB) interface on which no serial clock signal required. The disclosed portable data storage device utilizes a depacketizing method to decode a packet to obtain address information and controls a corresponding portable I/O device and data storage device according to the address information so as to achieve a goal for controlling two or more portable I/O devices and data storage devices. The USB interface, however, does not provide a clock signal and a chip selection signal and thus the disclosed portable data storage device can not be applied in serial bus devices that require a clock signal and a chip selection signal.
Another commonly used implementation for expanding is that data lines and clock signal line of the bus are shared while the chip selection line thereof is separated so that the chip selection line can be used to select any one of the serial bus devices. In such implementation, however, more slots are required for the host device to simultaneously support multiple removable electronic devices, increasing the hard ware cost. Moreover, it is also impossible to add more slots in a conventional portable electronic device since there is no room for more than on slot to be placed therein.